superstrate 996 dielectric constant?

Anybody know what dielectric constant range coors superstrates run? I found one spec sheet listing only the following minimal information:
εr=9.9 +/- 0.1 at 1 MHz
εr=9.9 at 4 GHz but no tolerance
εr=9.7 at 10 GHz but no tolerance

I am curious over a large manufacturing run what εr they seem to be able to hold over the 2-18 Ghz range.

A good high dielectric laminate (from Rogers Corp for example) do not have the tolerance at 10GHz higher than +/- 0.5%

http://www.rogerscorporation.com/mwu/pdf/3200data.pdf

Only the laminate manufacturer can tell exactly the Er variation vs Frequency (in volume production) because this is dependent by each material used.

I can only use Alumina ceramic for this design. Can not hold the dimensional tolerance required on a laminate.